The ability to grow large mammalian oocytes from the earliest follicular stages through to maturation and fertilisation in vitro would not only provide a model system to study the process of oocyte development in these species, it could potentially revolutionise fertility preservation practice in humans and animal production systems for cattle, for example. The production of live offspring from oocytes grown in vitro from the primordial stage has only been achieved in mice (Eppig and O'Brien 1996; O'Brien et al., 2003). This demonstration has led to a step wise development of similar culture systems for humans and domestic animals. Each of these systems support different stages of oocyte development.
In principle, primordial follicles are isolated from cortical tissue (often taken via biopsy), and grown into oocytes, which can then be fertilised. However, the different systems in the art are not necessarily designed to work together, and, therefore, such systems may not be compatible or may not provide a useful or efficient method of producing in vitro viable and healthy oocytes for later fertilisation, ultimately resulting in live offspring.
In addition, developing in vitro maturation systems for the development of primordial follicles into oocytes in larger mammals, such as human, bovine or ovine, for example, has been more difficult to achieve because of differences in scale of timing and size between rodents and larger mammals (Telfer and McLaughlin, 2012). These differences have led to low yields of viable and healthy oocytes from these systems.
Therefore, it is an object of at least one aspect of the present invention to provide a viable and practicable method of developing viable and healthy larger mammalian oocytes from primordial follicles.